In normal somatic cells, the telomere, which is located at the end of a chromosome, gets shortened at each time of cell mitosis. When the telomere is shortened to some level, the cell will lose the ability of replication and go into apoptosis stage. Telomerase, which is a ribonucleoprotein, acts on the telomere in a eukaryocyte, so as to prolong or maintain the length of the telomere. A telomerase mainly includes two portions; one is a protein sub-unit with activity of reverse transcription, i.e. the human telomerase reverse transcriptase (hTERT), and the other one is an RNA template for synthesizing repeated sequences of the telomerase, i.e. the human telomerase RNA component (hTR), wherein the RNA template includes the single RNA sequence, -AAUCCC, which is complementary to the telomerase sequence. Telomerase activity is rarely detected in normal human somatic cells, but is usually detected in the cells that keep proliferating, such as hematopoietic cells, embryogenic cells, stem cells, etc. It is estimated that about 85-90% of human tumor cells have telomerase activity, and that is the reason why tumor cells do not go into apoptosis like a normal cell and can keep proliferating (Urquidi et al., Annu. Rev. Med. 2000, 51, 65-79). Reductions in hTERT mRNA expression level and telomerase activity are observed during the processes of cell going aged or immortalized (Bestilny et al., Cancer Res. 1996, 56, 3796-802). Furthermore, the telomerase activity of a somatic cell that should not express the telomerase activity could be reproduced by introduction of the hTERT cDNA thereinto for a high level expression of telomerase activity (Bodnar et al., Science. 1998, 279, 349-52).
The telomere at chromosome ends of eukaryotic cells is guanine-rich. In normal physiological conditions, the single strand DNA of the telomere spontaneously forms a G-quadruplex structure. The G-quadruplex structure includes two portions, wherein one is a small loop composed of TTA, and the other one is a guanine-tetrad composed of four guanines formed by cyclic hydrogen bonds. In order to inhibit the differentiation of tumor cells, an alternative besides the direct inhibition to telomerase activity is to stabilize the G-quadruplex structure for inhibiting its reaction with the complementary single strand RNA (AAUCCC (SEQ, ID NO: 1)), so as to prevent the telomerase from extending the telomere. Chromosome replications of tumor cells may be inhibited by the mentioned method, so as to achieve the anti-caner effect directly or indirectly (Smogorzewska et al., Annu. Rev. Biochem. 2004, 73, 177-208).
It is observed in current studies that anthraquinone can stabilize the G-quadruplex structure for its formula with plane tri-cyclic structure. According to the researches to the quindoline derivatives (10H-indolo[3,2-b]quinoline) with tetra-cyclic structure, berberin with non-plane polycyclic structure and the analogs synthesized therefrom, it is known that the aromatic groups of the mentioned compounds play an important role in the bonding to the G-quardruplex structure. Over-expressions of known oncogenes usually induce cancers and are associated with many cell proliferation disorders, such as chronic lymphocytic leukemia, esophagus cancer, myeloma, etc. In additions, those genes also participate in many pathological and physiological processes. Many experiments have proved that over-expressions of tumor suppressor genes play important role in the prevention and treatment of tumors. Therefore, the research and development of the drugs for curing cell proliferation disorders can be applied in the cure of human cancers, just like the disclosures of Canadian Patent No. 2,428,206.
Although it has been published that a heteroannelated anthraquinone derivative can be synthesized by an acylation reaction of 1,2-diaminoanthraquinone to obtain a bis-substituent derivative, followed by a condensation reaction. However, this method only discloses the substituent of aromatic groups, and has a poor production rate (Peng et al., J. Org. Chem. 2005, 70, 10524-31).
Based on the above, the present invention provides heteroannelated anthraquinone derivatives and the synthesis method thereof, which is accomplished by preserving the chromophore group with plane tri-cyclic structure and the carbonyl groups at 9 and 10, which have better binding ability, then changing the tri-cyclic structure into tetra-cyclic structure and adding various side chains derived from different modified substituents, so as to synthesize a series of heteroannelated anthraquinone derivatives.